Multiplicity counting techniques are used to acquire time correlated data at high rates enabling processing of large volumes of signal pulse data into a more useable form. The technique is generally useful for high-speed processing of digital data and, in particular but not exclusively, for acquisition of neutron events during non-destructive mass assay of nuclear material, such as uranium and plutonium in many forms. During the fission process, multiple neutrons are emitted within a very short time frame, that is, in coincidence. The number of events detected in coincidence determines the multiplicity of the event.
In neutron multiplicity counting, voltage pulses corresponding to detected neutron events are inputted into a shift register that counts and processes the pulses. Counting and processing large volumes of neutron event data is required to minimize statistical errors.
U.S. Pat. No. 6,333,958, entitled “Advanced Electronics for Faster Time-Correlation Analysis of Pulse Sequences”, issued on Dec. 25, 2001 to Stewart et al. teaches that an accidentals register strobe generated from a fixed clock frequency can be used to replace the standard 5 ms accidentals strobe to improve the measurement precision of a shift register coincidence counter. This existing technology is very complex, requires many components to function properly and is prone to failures due to the complex interconnects. This technology is also very expensive to produce, and due to its slow speed (pulse rates greater than 4 MHz cannot be measured) cannot be used with today's high count rate instruments.
U.S. Pat. No. 4,920,271, entitled “Multiple channel programmable coincidence counter”, issued on Apr. 24, 1990 to Gaetano J. Amone. This coincidence counting device focuses on the minimization of dead-time using high speed clocks and parallel input channels. This device uses an antiquated Computer Automated Measurement and Control (CAMAC) data acquisition and control interface and therefore is difficult to use with current measurement instruments. One drawback of this device is that dead-time corrections cannot not be accomplished to correct measured counts for the front-end electronics dead-time.
U.S. Pat. No. 4,580,056, entitled “Neutron event counting circuit” issued on Apr. 1, 1986 to Kaiser et al, discloses a counting circuit which is a very simple system that will not work with today's modern neutron measurement systems. This system implements a one-shot multivibrator circuit for a front-end noise filter which will lead to increased loss in input pulses. This system counts both totals events and correlated events but does not count multiplicity events.
The multiplicity counters of the prior art are expensive, complex, and are unreliable due to their complexity. Also, due to their limited maximum input rate, these counters cannot be utilized effectively with high rate count instruments.